Data communication system

ABSTRACT

According to the inventive method, data from at least one ISDN data link, at least one conventional telephone link and at least one broadband data link, respectively, are transmitted in an SDSL frame of an SDSL data link, with the required control data being transmitted in either the eoc or in one or more Z channels.

[0001] In a traditional ISDN basic access, a two-wire data link isexclusively used for the ISDN service (see FIG. 1). To be able to makebetter use of existing two-wire data links between a network node and anetwork termination at the subscriber, a number of services aretransmitted simultaneously on one link, for example interleaved in aframe structure, in DSL (Digital Subscriber Line) links having a highertransmission rate. For the discussions following, data transport bymeans of an SDSL (Symmetric Digital Subscriber Line) frame isconsidered. It is known that within this frame, for example, the data ofone or more broadband links and of one or more ISDN or one or moreconventional telephony links can be transmitted. It is also known that,for these links, the information content of the operational bits can betransmitted in the eoc channel present in the SDSL frame.

[0002] The invention is based on the object of specifying another methodfor transmitting the operational control bits of a data link.

[0003] According to the invention, the object set is achieved by patentclaims 1 to 4.

[0004] The invention brings with it the advantage that the informationcontent of the operational bits of all links of the data frame can alsobe processed and transmitted at the correct time especially in thoseapplications in which accelerated processing and transmission of theoperational information is required.

[0005] The transmission of the call control in one or more Z channelsrequires little time, as a result of which time-critical features suchas, for example, calling line identification presentation can betransmitted at the correct time even when a large number of telephonycalls are simultaneously transmitted.

[0006] Further advantageous embodiments of the method are specified inthe further patent claims.

[0007] Further special features of the invention will be found in thesubsequent, more detailed explanations of an exemplary embodiment and bymeans of drawings, in which:

[0008]FIG. 1 shows an embodiment of an ISDN link,

[0009]FIG. 2 shows an embodiment of an SDSL network termination,

[0010]FIG. 3 shows the structure of an SDSL frame,

[0011]FIG. 4 shows an exemplary embodiment of the structure of an SDSLframe,

[0012]FIG. 5 shows an addressing field,

[0013]FIG. 6 shows a further exemplary embodiment of the structure of anSDSL frame.

[0014]FIG. 1 illustrates an ISDN link between a terminal TE and anetwork node LT. Between a line terminating unit LT constructed, inparticular, as a switching node and a network terminating unit NTarranged at the subscriber, two-wire connecting lines are used.

[0015]FIG. 2 shows an SDSL link between a second network terminatingunit NT, a network node LT and terminals E1, E2 and E3. In the networknode LT, the data for the terminals are supplied or taken, respectively,from a narrow band and broadband network via corresponding gateways andare combined in the SDSL frame. The narrow band and broadband data ofthe SDSL frame are transmitted synchronously in time-division multiplexbetween a first line terminating unit LT and the network terminatingunit NT. The combining at the transmitting end and the splitting up atthe receiving end of the data belonging to the narrow band or/andbroadband network is performed in accordance with the known methods ofdigital time-division multiplexing in the SDSLM module which can also bereferred to as a transceiver. In the network terminating unit NT, thebroadband data are forwarded to a broadband controller. The narrow banddata are forwarded to a narrow band controller which forwards therelevant data to the downstream a/b controller for the conventionaltelephone connection or to the S₀ controller for the ISDN connection.

[0016] The network terminating unit NT can be connected to one or morebroadband terminals and one or more ISDN systems or, respectively, oneor more conventional telephone sets. Each individual telephony, ISDN orbroadband link is in each case associated with its own a/b, S₀ orbroadband controller.

[0017] By way of example, the terminal type E1 is a conventionaltelephone, the terminal type E2, as an alternative, is an ISDN systemand the terminal type E3 can be a data processing system.

[0018]FIG. 3 shows the previously known structure of an SDSL frame. TheSDSL frame is subdivided into preferably four payload blocks PL1, PL2,PL3 and PL4. Each payload block PL1, PL2, PL3, PL4 can be subdividedinto 12 subblocks P01 to P12, P13 to P24, P25 to P36 and P37 to P48.Each subblock can be subdivided into 1 to 8 Z channels having in eachcase 8 kbit/s and 3 to 36 B channels having in each case 64 kbit/s.

[0019]FIG. 4 shows by way of example a frame structure for a utilizationof an ISDN link. The data of the B1 and B2 channels of an ISDN link arepreferably combined in two 64 kbit/s B channels of an SDSL connectionand the signaling data of the D channel are combined in two 8 kbit/s Zchannels. The remaining area of the subblocks of the SDSL frame is usedfor further payload data from, for example, a number of ISDN links or,for example, one or more conventional telephony links or one or morebroadband links. In this sense, the remaining 6 B channels of the SDSLframe in the exemplary embodiment of FIG. 4 are combined to form a 384kbit/s broadband link which is available simultaneously with the ISDNlink. In this example, the operational control bits for both links aretransmitted in the eoc channel.

[0020] The digitized data of one or more analog telephony links aretransmitted in 64 kbit/s channels and in each case precisely one Bchannel is allocated to one conventional telephony link. The data of oneor more broadband links are combined in the number of B channels neededin each case. In this arrangement, only the upper limit of the number ofB channels defined in FIG. 3 must be adhered to.

[0021] In the overhead section OH (see FIG. 3) of the SDSL frame, theSDSL overhead data are accommodated which contain status information andan embedded operations channel (eoc) channel, with a transmission rateof about 3.3 kbit/s for operating the SDSL transmission link.

[0022] In addition, the SDSL frame contains a 14-bit-wide sync word atthe beginning for synchronization and two spare bits at the end of theframe.

[0023]FIG. 5 shows a previously known example of an addressing field ofthe eoc address extension necessary for addressing the individual ISDNlinks or conventional telephone links and broadband links. This addressfield exhibits the components service ID and service No. which arenecessary for unambiguously addressing the respective link. In thisarrangement, a certain service No. is addressed within a service type(e.g. one of a multiplicity of ISDN links).

[0024] In a further exemplary embodiment according to the invention, theoperational control bits for the SDSL transmission link,, particularlythe call control bits for one or more telephony links, are transmittedin one or more 8 kbit/s Z channels. As a result, this information can betransmitted to the remote line end of the SDSL link at least 2.5 timesfaster than in the conventional eoc channel. The resultant gain in timeis decisive for simultaneous control of a multiplicity of conventionaltelephony links at the correct time via a common SDSL transmission link.

[0025]FIG. 6 shows an exemplary embodiment according to the invention inwhich the digitized data of three conventional telephony links arecombined in three B channels with in each case 64 kbit/s, and theassociated call control bits are combined in one Z channel with 8kbit/s, within an SDSL frame The number of telephone links operatedsimultaneously on an SDSL link can still be increased considerably sincethe SDSL frame according to FIG. 3 can include up to 36 B channels andup to 8 Z channels.

[0026] At present, applications of this type have once again gained theinterest of the network operators since they can be implementedparticularly inexpensively with the symmetric time-division multiplexstructure of the SDSL system and since the conventional telephonyservice is still head of the multimedia services by a wide margin withregard to the amount of utilization. In this connection, the objectarises to render visible particularly time-critical features of thetelephony service such as, for example,, calling line identificationpresentation, at the correct time even with a high call loading due to amultiplicity of telephony connections.

[0027] In the embodiment according to the invention, these objects areachieved with the transmission of the call control bits in one or more Zchannels.

[0028] In a further embodiment of the invention, a switch-over betweenthe use of the eoc channel, on the one hand, and one or more Z channels,on the other hand, for the operational. control bits is effected asrequired during the start-up procedure. This is of advantage, forexample, if it is intended to guarantee that time-critical conditionswill be adhered to for a multiplicity of simultaneous telephonyconnections or if the time conditions in the eoc channel are sufficientfor only one or a few telephony connections to be operatedsimultaneously and the Z channels becoming available are also to be usedfor transmitting user data.

[0029] In a further advantageous embodiment, the same message format asin the eoc channel is used for message coding and addressing in the eocchannel and in the Z channel or channels. This particularly simplifiesthe circuitry for the operational change between using the eoc channeland the Z service channel or channels.

[0030] In a further embodiment, the use of the eoc channel or of the Zchannel or channels and the use of the individual subchannels of theSDSL frame in the terminating unit at the far line end, preferably inthe network terminating unit NT, is defined within the start-upprocedure during the SDSL connection set-up by the LT unit.

1. A data communication method, in which the data of all types ofterminals, together with the associated operational control bits, aresynchronously inserted into the frame (SDSL) in digital time-divisionmultiplex, and are transmitted in a transceiver unit SDSLM for insertingand splitting up data from terminals of types E1, E2, E3, characterizedin that the operational control bits are allocated to one or more Zchannels of the SDSL frame.
 2. The method as claimed in claim 1,characterized in that the operational control bits are allocatedswitchably either to the eoc channel or at least one Z channel.
 3. Themethod as claimed in one of the preceding claims, characterized in thatin each case the same message format is used for message coding andaddressing, respectively, in the eoc channel or in the Z channels. 4.The method as claimed in one of claims 1 or 2, characterized in that theallocation of eoc or Z channels and the use of the individualsubchannels of the SDSL frame is signaled to the terminating unit at thefar line end and, as a result, is defined in the terminating unit,within the start-up procedure during the SDSL connection set-up.